We seek to understand the mechanisms by which biological macromolecules recognize their partners in the formation of functional macromolecular assemblies that are critical to human health. Molecular recognition plays a central role in most, if not all, cellular processes. Failed recognition events have been implicated in numerous disease states, ranging from flawed control of long and short range signaling and cellular proliferation, to defects in important metabolic activities. Success in this endeavor will enable the discovery of new and better human therapeutics. One Specific Aim centers on the cytochrome P450s involved in the human metabolism of drugs (CYP3A4, CYP2C8) and the biosynthesis of estrogens in normal and cancerous tissue (GYP19). CYP3A4 is the major P450 expressed in human liver and represents the main route for xenobiotic clearance, metabolizing approximately 50% of the Pharmaceuticals ingested by man. CYP2C8 plays an important role in the metabolism of a number of therapeutics, such as the anticancer drug taxol, antimalarials, anti-diabetics and the cholesterol lowering statins. A second Aim focuses attention on the human G-protein coupled receptors (GPCRs). GPCRs account for a large fraction of marketed drugs designed to modulate homeostasis, including vision, smell, vascular tone, and neurosignaling. Initial work will focus on the B2adrenergic receptor that activates adenylyl cyclase through action of the stimulatory family of G-proteins upon catecholamine binding. This receptor is found in vascular and airway smooth muscle, functions in vaso- and broncho-dilation and is implicated in cardiovascular disease and asthma. Systematic investigations are proposed that focus on the major classes of recognition events in biological systems: Protein-protein recognition, defining the specificity and affinity of higher order oligomeric states that effect enzymatic metabolism and receptor signaling; Membrane recognition, understanding the role of the complex component mix (phospholipids, fatty acids, cholesterol) effecting receptor and enzyme activities; Protein- small molecule recognition, ascertaining multi-component interactions which regulate agonist, antagonist and reverse agonist effects and metabolic homo- and hetero-tropic cooperativity.